Honestly, I do not think there is a way to render this quotations as anything but contradictory. Blake was intentionally rebelling against this exact type of thinking when he wrote The Marriage of Heaven and Hell.

Both quotes do relate to Gatsby however and don't necessarily clash there. Gatsby teaches Nick a lesson and without the huge excesses of Gatsby's character, Nick may not have learned what he did about the human cost of such ambition.

Blake's quote could be understood as learning from our mistakes. If we live a life of excess, eventually we will fall. Blake was a strong Christian man who used his faith to show how his narrators/characters in his poems would make it to Heaven for their good deeds. Those who did not would suffer or fall. I can see this quote tying into Fitzgerald's themes as well. Those who take advantage of others and take more than they need will eventually get what's coming to them.

Aristotle then says something very similar in his quote. If we don't get too greedy, and we moderate everything in our lives, we will be happy and live full lives. We must use moderation, for anything more than that is not only greedy, (which is sinful), but it is also wasteful. So this too applies to the same theme Fitzgerald used. Fitzgerald saw the "crash" coming long before anyone else did. Using such quotes in the Great Gatsby would make sense. Had the destructive East Egg people lived in moderation and not used materialistic items and people in excess, there would not have been any deaths in the end of the novel.

Blake's quote could be understood as learning from our
mistakes. If we live a life of excess, eventually we will
fall. Blake was a strong Christian man who used his faith to
show how his narrators/characters in his poems would make it to
Heaven for their good deeds. Those who did not would suffer
or fall. I can see this quote tying into Fitzgerald's themes
as well. Those who take advantage of others and take more
than they need will eventually get what's coming to them.

Aristotle then says something very similar in his quote.
If we don't get too greedy, and we moderate everything in our
lives, we will be happy and live full lives. We must use
moderation, for anything more than that is not only greedy, (which
is sinful), but it is also wasteful. So this too applies to
the same theme Fitzgerald used. Fitzgerald saw the "crash"
coming long before anyone else did. Using such quotes in the
Great Gatsby would make sense. Had the destructive East Egg
people lived in moderation and not used materialistic items and
people in excess, there would not have been any deaths in the end
of the novel.

Moderation is a virtue unto itself. How would you like to have a
moderately faithful wife? or a moderataely honest business
partner?